One of the more controversial statements made by Chazal is "Our holy fathers all kept the entire Torah". We are told, for example, that Avraham Avinu kept the entire Torah and all rabbinic enactments right down to eruv tavshilin. Many people take these statements literally. Far too many.
The objections to the statement range from the obvious to the subtle. For the obvious, how could the Avos observe the Torah when it hadn't been given yet? How could they celebrate going out of Egypt from slavery to freedom if they were never slaves? How could Avraham Avinu, a"h, serve the angels who visited him milk and meat? How could Yaakov Avinu, a"h, marry two sisters? It's a mitzvah in the Torah to put a parapet around one's roof. Our Avos lived in tents. Did they build sukkos every autumn?
I believe that to best understand Chazal's statement one must understand what "Torah" is. We are so used to using Hebrew words as labels in English that we forget they have real meanings. For example, Torah means "teaching" or "instruction". It is God's communication to us as to His expectations for us in this world. It is not simply the scroll we read from three times a week or the collected knowledge in all the seforim in the world. As Chazal note, it is indescribably huge, greater than we can ever understand being the produce of the Divine intelligence.
Another support for this position can be found in the words of Chazal where they note that Torah preceded the Creation of the world. As Chazal say, God looked into the Torah to create the world. Now, unless one is simplistic enough to think that there was this one original scroll floating out there from the ether before the universe came into being, one must conclude that Torah is the blueprint for Creation, the framework for all existence, the answer to the question of Life, The Universe and Everything.
This helps to explain how our Avos "kept" the whole Torah. The "whole Torah" doesn't mean performing the Taryag mitzvos but rather it means participating in the progression of history in total consonance with God's plans. The Talmud tells us that history moves forward towards a purpose. There will be a completion of the Final Redemption, there will be a Moshiach and there will be an Olam Haba in this reality. For us, participating in this progression is accomplished by the performance of the mitzvos. Through limud Torah and engaging in activities that sanctify God's name and fulfill His will we move reality forward towards its ultimate destination.
Our Avos worked on the same goal but it is important to remember that they were on a level so much higher than us that we cannot comprehend how they interacted with reality. Every autumn, as the Torah reading cycle returns to their histories I see articles getting published about them that attempt to humanize them to a ridiculous degree, commenting on whether or not they existed, criticizing their parenting techniques, wondering about their connection to religions that have no real connection to them. Take a step back and think about it: these men spoke with God. They didn't just worship Him. They weren't just highly aware of Him. They had communication with Him. How can we hope to understand men like that?
The Nefesh HaChaim notes that because of this heightened spirituality they were therefore able to guide all their actions in harmony with the will of God. Avraham Avinu didn't simply feed the angels who visited him what he did because that's what was in the pantry that day. Yaakov Avinu didn't marry two sisters because he had no Torah. In all their actions they recognized what the right course was to take to move history forward and they took it. These decisions, for whatever the reason was to the Divine will, were those that were necessary even if later on the halacha would forbid them. For us, marrying two sisters is an abomination. For Yaakov Avinu it was the step he had to take to bring forth the founders of our nation.
With this understanding we can now see how our Avos kept "the whole Torah" and it serves as a reminder to us that there is a purpose to our practice. We are not simply to perform mitzvos out of rote or habit but to keep our minds on the bigger picture, on the grand purpose behind all our actions. We must bring meaning into our actions and understanding how our Avos did it helps to serve as a guide.